The present invention relates to solutions for winding coils of stators that are used in induction motors. More particularly, the invention relates to winding wire coils with turns that have different lengths and inserting the completed coils into stator core slots.
Electric motors generally include two main parts--a fixed hollow portion known as a "stator" and a portion that rotates inside the stator, called a "rotor" or an "armature." Electrically conducting coils of wire are typically wound in longitudinal slots on the stator. Rotors are configured in many different ways, but they are also wound with electrically conducting wire. Current supplied to the rotor wires interacts with a magnetic field that is produced in the stator to create the torque that is required to operate the motor.
Wire coils are typically formed by winding wire around a pair of the longitudinal slots described above. Sections of the wire coils typically span across the end of the stator where they exit one slot and enter the other. Filling the slot with wire generally requires placing some turns deeper inside the slot (i.e. further away from the central axis of the stator core) than others. In the most common winding methods, all turns of wire in the coil are formed with approximately the same length of wire. The length of wire that is used during winding is that which is required to form the longest turns--those that will be placed furthest away from the axis of the core. As a result, the turns that are placed closer to the central axis usually have more wire than they need to be routed through the portions of the slot where they rest. This means that there is more slack in those turns that are placed closer to the center of the core than there is in those that are more deeply inserted.
At least one existing device is capable of forming wire coils with turns that have different lengths. An apparatus that may accomplish such a task has been described in U.S. Ser. No. 09/348,551 filed Jul. 7, 1999, now U.S. Pat. No. 6,206,052, the contents of which are hereby incorporated by reference in their entirety. In such a device, wire is wound around a template while its sections are moved toward or away from each other in a direction orthogonal to the longitudinal axis of the template. Moving the template sections apart during winding forms a larger wire turn, while moving them together forms a smaller wire turn.
The present invention proposes new solutions for forming coil turns with varied lengths and for placing completed coils that are made from such turns into stator core slots. In one embodiment, the relative positioning of the sections of a template are altered as wire is wound around the template. As described earlier, altering template positioning during winding enables the turns to be formed with different lengths. These varied length turns are gathered to make the completed coils.
According to an aspect of the invention, wire turns are deposited on an insertion tool in an order that is dependent upon the length around the longitudinal slot pair at the depths at which it is desired to place the turns. More specifically, wire turns will be deposited on the insertion tool in an order that is dependent upon their respective lengths. These respective lengths will, in turn, be dependent upon the distance around the slot at the depth at which it is intended to place the turn. The turns are placed between rods that are positioned to match predetermined angular locations of the stator slots, and the completed coils are pushed along the rods and into the appropriate pair of slots on the stator core.
The present invention can be used to form a coil with varied length turns, and to position the turns in each coil such that they rest at the depth inside the slot that is most appropriate for their lengths. Turns will preferably rest at the location inside the slot that will use substantially the entire length of the wire turn in routing the wire between the slots and around the stator core. Tension in each wire will preferably be optimized. That is, the amount of tension in each wire will preferably be high enough to form turns without slack, while being low enough to avoid pulling and stretching the wire.